It has recently become known that perforated sheet with an image and/or reflective surface on one side is a highly attractive advertising medium. Such material is transparent from one side while its image can be seen from the other side provided the level of illumination is greater on the image side of the sheet. Previously, painted dots over a transparent sheet material were used to create the equivalent effect as disclosed in U.K. Patent Application No. 2,118,096 A by Hill et al. and U.S. Pat. No. 4,673,609 issued to Hill. Obviously, the placement of such dots of about 1.0 mm in diameter with a spacing of 1.4 mm between centers requires precise registration and involves special masks. Hill '609 does mention punching, burning, and laser cutting to obtain the perforations but discloses no techniques by which laser cutting can be achieved.
The conventional methods of making perforations in plastic sheet material is to first make a die of a desired pattern and then to punch the material with this die over the surface of the material. In order to cover a large sheet material with holes it is necessary either to make a very large and expensive die or to punch the material several times. Multiple punching requires careful alignment of the sheet material before each punching step. Any slight misalignment becomes highly visible in the final product.
A second disadvantage is that not all material is amenable to being punched. For example, there are highly reflective materials which have tiny glass beads on their surface that would prevent mechanical perforation or dull the dies used to make these perforations. A second problem faced by mechanical dies is their tendency to become clogged with glue when perforating vinyl. Unfortunately, most commonly available vinyls have glue on one side. One possibility of overcoming the problem which are present for mechanical dies is to utilize a laser to perforate sheet material. It is known to cut holes in metal plate using lasers. However, obviously powerful lasers are required to accomplish such a task. For purposes of cutting through sheet material lower power lasers would be adequate but the cost of a laser powerful enough to burn through a variety of different sheet material of different thicknesses with a hole of a varying diameter as required for different purposes would still be relatively expensive.